Incandescent electric lamp



March 21, 1939.

J, M KENDALL INCANDEISCENT ELECTRIC LAM? Filed Dec.

IN ENTOR ATTORNEYS.

Patented Mar. 21, 1939 UNITED STATES PATENT OFFICE physical Research Corporation,

New York,

N. Y., a corporation of New Jersey Application December '28, 1938, Serial No. 248,042

Claims.

This invention relates to incandescent electric lamps and more especially to a. special form of incandescent lamp for use in recording galvanometers. Such lamps contain a straight filament 5 and light from the filament is reflected by the galvanometer mirror to the light sensitive recording tape on which it is focused to produce a point image of the filament. So-called ghost images of the filament are produced by light rays reflected from the interior surface of the light bulb to the galvanometer mirror and such ghost images render the record on the tape less distinct than would otherwise be the case.

An object of this invention is an incandescent electric lamp suitable for use with a galvanometer in which provision is made for preventing the production of the ghost images above referred to.

In a lamp embodying the invention, there is provided the usual straight filament and associated with it is a reflector having two angularly related parts, each part being parallel to the filament and being so arranged that light rays from the filament are reflected from it away from the plane defined by the filament and the vertex of the angle formed by said reflector parts. With this arrangement, the only light which reaches the galvanometer mirror is light passing directly thereto from the filament. All the light rays which might be reflected from the interior surface of the bulb to the galvanometer mirror are intercepted by the reflector and directed out of the bulb at such angularity that they cannot strike the galvanometer reflector.

Other objects, novel features and advantages of this invention will become apparent from the following specification and accompanying drawing, wherein:

Fig. 1 is a side elevation of a lamp embodying the invention;

Fig. 2 is a similar view at right angles to Fig. 1,

and

Fig. 3 is a plan view of Fig. 2.

The lamp comprises an enclosing bulb l0 preferably of the same shape as heretofore used in which is arranged the usual stem I l with leadingin or supporting wires l2 and I3 sealed therein. The supporting wire l3 extends nearly to the end of the bulb whereas the supporting wire I! terminates a short distance beyond the end of the stem H. To the end of the supporting wire I2 is connected a spring I! which is a conductor of electricity and between the spring I4 and the end of the supporting wire I3 is connected the straight filament IS. The construction heretofore described has been in regular use in galvanometer lamps for sometime past and does not embody applicants invention.

The novelty in the present invention resides in the reflector I6 supported by the wire l3. Preferably, the reflector l6 consists of a thin 5 plate of polished metal arranged to provide two surfaces angularly related with respect to each other. The reflector is attached to the supporting wire l3 along the vertex line of the angle formed by the two surfaces, and the arrangement 10 is such that each surface forms an angle of more than with the plane defined by the filament and said vertex line. One of the two surfaces consists of a single thickness of the metal plate while the other surface consists of two thicknesses 15 formed by doubling a portion of the metal plate back upon itself. This surface is slightly larger than the first-mentioned surface so that it overlies the vertex line above referred to.

Light rays passing to the reflector from the fila- 20 ment are reflected away from the plane defined by the filament and vertex line so that they emerge from the bulb outside of the arc defined .by the points A and B. A curved surface is present along the vertex line which would normally reflect light from the filament through the arc AB. However, the fact that one surface extends beyond the vertex line prevents such reflection from the curved portion. The edge of the overlapping portion of the reflector can easily be made very sharp so that it will reflect an inappreciable amount of light.

Although the reflector has been shown as composed of a single strip of polished metal, it is to be understood that it may be made up of two 35 plates suitably joined together. However, the arrangement shown is preferred, inasmuch as it is easier to construct and assemble than would be the case if it were made up of two separate plates.

Moreover, while the reflecting surfaces preferably are parallel to the filament, it is within the contemplation of this invention that there may be other relationship between the filament and the reflecting surfaces so long as the surfaces are so arranged as to reflect light rays outside of the arc defined by the point A-B. Preferably, the angle between each reflector and the plane defined by the filament and the vertex line of the reflector is but may be varied to meet con- 50 ditlons, it being understood that this angle is always greater than 90 but seldom, if ever exceeds I claim:

1. An incandescent electric lamp comprising a 55 bulb, a filament therein, and a reflector mounted within said bulb behind said filament, said reflector having two ang'ularly related surfaces so arranged that light rays from the filament are reflected thereby away from the plane defined by the filament and the vertex line of said reflector.

2. An incandescent electric lamp comprising a bulb, a filament therein, and a reflector mounted within said bulb behind said filament, said reflector having two angularly related surfaces, each being parallel to said filament and making an angle not less than 90 with the plane defined by said filament and the vertex line of said refiector.

3. An incandescent electric lamp comprising a bulb, a filament therein and a reflector mounted within said bulb behind said filament, said reflector having two angularly related surfaces s0 arranged that the angle therebetween facing said filament exceeds 180.

4. An incandescent electric lamp according to claim 3 characterized by having the reflecting surfaces parallel to said filament. I

5. An incandescent electric lamp according to claim 1 characterized by having the reflecting surfaces parallel to said filament.

JAMES M. KENDALL. 

